Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the burden and does disclose the paid model (0.003 USDC per call via x402) and the data source (RDAP), which are real behavioral traits. It omits not-found/error behavior, rate limits, and latency, so it falls short of full disclosure.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences, zero waste: the capability and returned fields come first, the pricing condition second. Nothing is padded or restated from the schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter tool with no annotations and no output schema, the description usefully enumerates the response fields and the cost basis, which is most of what an agent needs. It stops short of covering failure cases (unregistered domain, RDAP lookup failure) or how results are cached.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and both parameters (domain, paymentProof) are documented in the schema, including the omitting-the-proof-then-retrying flow. The description adds no syntax or format detail beyond that, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (looks up) and resource (a domain via RDAP) and then enumerates exactly what comes back: registrar, creation/update/expiry dates, domain age, status codes, nameservers. That field list distinguishes it from dns_lookup and domain_email_security without opening their schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied by the RDAP/registration-data framing; there is no explicit statement of when to pick this over dns_lookup, domain_email_security, or address_check, and no exclusions or prerequisites beyond the payment note.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.